The present invention relates generally to systems for mixing gases and liquids and is more particularly concerned with a new and improved bubble injection system for forming and distributing bubbles in a body of liquid.
For some time spargers have been used as a means of dispersing gases in liquids for various purposes, such as heating large amounts of liquid using live steam, or maintaining constant agitation of the liquid in foam flotation processes using compressed air or gas. A sparger generally consists of a pipe having a plurality of small perforations or nozzles spaced at regular intervals along its length. The pipe typically is submerged in the liquid to be treated and gas is introduced into the pipe and forced to bubble through the holes or nozzles therein into the liquid. While this type of sparger is relatively inexpensive, it is not capable of producing very fine bubbles or of providing a broad and uniform distribution of the bubbles within the liquid body. In order to accomplish this, it is frequently necessary to further agitate the liquid mass thereby significantly increasing the cost of the equipment and the energy expended in order to provide the desired bubble distribution.
Smaller or finer size bubbles can be generated in a liquid stream in an energy efficient manner by the use of porous metal tubing positioned within a conduit through which the liquid passes. The gas is pumped though the porous wall of the tube while the liquid flows therealong. The bubbles formed in the liquid at the wall of the porous metal tubing are drawn away from the wall and are carried with the flowing liquid to their point of use, typically at a remote location from the point of bubble formation. Unfortunately, the small bubbles entrained within the liquid tend to combine forming larger bubbles and also tend to separate from the liquid when any attempt is made to convey the bubble/liquid mixture to a location remote from its point of origin. Thus, the distribution of very fine bubbles over a large area is extremely difficult.
It has been found in accordance with the present invention, that the aforementioned problems and difficulties can be resolved by the utilization of a bubble injection system that combines the beneficial aspects of the prior techniques while avoiding the draw backs thereof. This is achieved through the use of a system employing separate conduits having a plurality of porous tubular outlets forming jet ports at spaced intervals along the conduits whereby the gas and liquid phases are isolated from each other until just before they reach their point of use. At that location they are combined to form micron size bubbles at the jet ports and the liquid/bubble mix is immediately injected into the body of liquid being treated. The system of the present invention specifically comprises an axially extending inner liquid carrying conduit, a concentric outer conduit extending axially along the inner conduit and spaced therefrom to provide a gas channel therebetween and a plurality of porous tubular outlets extending generally radially from the inner conduit to the outer conduit across the gas channel and terminating in outlet jet ports that are spaced along the longitudinal extent of the outer conduit. The inner conduit defines an axially extending liquid flow channel that directly communicates with the jet ports through the outlets so that when the gas flowing through the gas channel penetrates the porous tubular outlets to initiate the formation of gas bubbles on the walls of the outlets, the liquid flowing through the liquid conduit and outlets will strip the partially formed gas bubbles from the surface of the outlets and sweep them out of the jet ports for immediate dispersion within the body of liquid being treated.
Bubble injection systems of the type described are particularly well suited for use in chemical reactors, gas flotation apparatus for ore separation, the processing of precious metals, coal flotation processes, for the introduction of air into bacterial reactors, fish farming ponds and the like and sewage treatment facilities. The effectiveness of the system of the present invention relies upon the separation of the gas and liquid phases until immediately prior to the point of injection of the bubbles into the system and the utilization of ultrafine or micron size gas bubbles resulting from the stripping or shearing of the bubbles from the porous outlet surfaces before full bubble formation has been achieved. These features coupled with control of both the liquid and gas pressure as well as the diameter of the jet ports facilitate improved dispersion of the micron size gas bubbles throughout the entire body of treated liquid. Further, the simplicity of the design significantly enhances heat transfer and reduces installation and maintenance cost while permitting extensive flexibility therein.
Other advantages and features will be in part obvious and in part pointed out more in detail hereinafter.
A better understanding of the objects, advantages, features, properties and relationships of the invention will be obtained from the following detailed description and accompanying drawings which set forth an illustrative embodiment and are indicative of the way in which the principles of the invention are employed.